One well-known type of high speed band printer comprises a flexible endless type band supported by spaced drive pulleys adjacent a row of uniformly spaced print hammers at a print line. An electric motor drive rotates the drive pulleys so that the type band moves at a substantially constant speed depending on the desired printing speed relative to the row of print hammers. Type characters on the band are arranged in a single row and are uniformly spaced with a pitch differing from the spacing or pitch of the print hammers so that mutual alignments of the type characters and print hammers occur in scan and subscan sequences. An electronic print control which includes type position circuitry selectively operates the print hammers in timed relation with the motion of the print characters at the given band velocity to print characters at desired print locations of the print line. Timing signals for operating the type position circuitry to actuate the print hammers at the correct time are provided by a stationary timing transducer which senses timing marks movable with the type band. The timing marks are typically fixed directly on the band in a single row or track called an emitter track parallel with the row of type characters. The timing marks are fixed on the band at a known distance from each other and in a known relationship to the type of characters usually with the same spacing as the type characters. Thus the emitter or timing signals generated by the sense transducer represents scan signals useful by the print control for operating the type position circuitry for the purpose of indicating type characters available to be printed as well as for other timing functions.
To print correctly, the printing controls must operate in synchronism with the moving type characters. That is, the character signals generated by the type position circuitry must agree with the type characters as they are moving toward alignment with the print hammers selected to be actuated. One means for achieving synchronization of the print controls employs a reference transducer means which generates a home or reference signal when a reference character is at a predetermined location relative to a given print hammer. The reference transducer means generates the reference signal by sensing one or more reference marks indicative of the reference character and movable with the type characters and timing marks. The reference marks are usually fixed relative to or on the type band in a known relationship to a given timing mark sometimes called the true home timing mark at a known distance relative to the reference character, usually the first character of the type set. The reference transducer means is located to sense the reference mark and to generate a reference signal when the reference character is at a predetermined lead distance from a position of alignment with a given print hammer. The lead distance is dependent on the type band or type character speed and the hammer flight time actual or effective of the given hammer. The lead distance corresponds to the distance the reference character must travel at the type band speed in the given flight time interval in order to become aligned with the given print hammer at the instant of impact.
The means for achieving synchronization usually employs sync control circuitry activated by the reference signal which counts timing signals between reference signals and at reference signal time generates a sync control signal which is used to activate the print controls to initiate printing. Thereafter, the synchronization control operates at reference signal times for determining whether the type position position circuitry is generating a reference character signal. In the event the type position circuitry is not generating a reference character signal at reference pulse time a sync control pulse is generated for use to discontinue printing and or to indicate an error.
With such an arrangement, changing type speeds to enable the printer to be operated at plural different printing speeds to achieve printing at different print rates presents a problem. This is simply because of the fact that different lead distances are required for different type speeds where the flight time of the given hammer remains the same. One option for accomplishing lead distance change might be to physically change the position of the reference transducer. Another option is to change the position of the reference mark relative to the reference character. A third might be to provide multiple reference marks located at different distances relative to the reference character. A fourth option might be to replace the control circuitry to function for different reference characters. All of these options have serious drawbacks such as increased cost, structural complexity and opportunity for error upon operator intervention. In addition, none of the above options allow complete flexibility in the choice of speeds. This is due to the fact that the lead distance for certain speeds is at a position which is not equal to an integer number of timing or emitter marks.
The present invention avoids the above drawbacks, does not require require physical rearrangement or replacement of components for its complete flexibility in the choice of operating speeds.